1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine that can be run even with a blended fuel of various compositions of alcohol (single component) and gasoline. In particular, the invention relates to a technique in which a concentration of a single component is estimated based on an air fuel ratio correction component, and an amount of fuel to be injected is optimized by the use of the estimated concentration value of the component.
2. Description of the Related Art
In recent years, motor vehicles or automobiles called FFV (flexible fuel vehicle) have been developed which become able to run even with a blended fuel of various compositions of alcohol and gasoline, other than with gasoline alone.
In this case, alcohol has a content of C (carbon) atoms differing from that of ordinary gasoline (blended fuel), so when a blended fuel of alcohol and gasoline is supplied to an internal combustion engine used for FFV, it is necessary to adjust the amount of fuel to be injected according to an alcohol concentration in the fuel.
In such a kind of FFV, there has conventionally been proposed, as an internal combustion engine control apparatus for estimating an alcohol concentration in fuel, a technique that estimates an alcohol concentration from a correlation between an air fuel ratio feedback correction coefficient, which is calculated based on an air fuel ratio AF in an exhaust gas derived from an air fuel ratio sensor, and the alcohol concentration (see, for example, a first patent document: Japanese patent application laid-open No. 2004-245097 and a second patent document: U.S. Pat. No. 6,016,796).
In general, when an alcohol concentration in a blended fuel is changed by refueling, there will be a transportation delay until the blended fuel in a fuel tank with its alcohol concentration thus changed arrives at an injector that supplies the fuel to an internal combustion engine, and this delay becomes larger in a returnless fuel supply system.
In a general returnless fuel supply system as shown in a block diagram of FIG. 12, fuel in a fuel tank 20 is sent to a fuel supply pipe 25 through a fuel pump 22 and a pressure regulator 23, and thence is further introduced into a delivery pipe 26, so that it is injected from injectors 21 to an internal combustion engine at appropriate injection timing.
At this time, fuel in a downstream side of the pressure regulator 23 advances only by an amount of fuel injected by the injectors, so a delay in the change of the alcohol concentration is large, but in an upstream of the pressure regulator 23, fuel is always circulated in the following path or route, i.e., the fuel tank 20→the fuel pump 22→the pressure regulator 23→the fuel tank 20, so the delay of the alcohol concentration change is very small.
Therefore, the delay of the alcohol concentration change from the fuel in the fuel tank 20 to the fuel in the injectors 21 is represented by a fuel transportation delay of the fuel supply pipe 25 and a fuel transportation delay of the delivery pipe 26 at the downstream side of the pressure regulator 23.
Here, the delay in the relatively long thin fuel supply pipe 25 becomes a dead time delay, but the delay in the relatively thick fuel supply delivery pipe 26 becomes a first order delay because fuel mixes in the delivery pipe 26.
These dead time delay and first order delay change in inverse proportion to the flow rate of fuel, and are represented, if organized according to an accumulated or integrated amount of injection, by a predetermined function.
FIG. 13 is a waveform chart that shows the delay of the alcohol concentration change comprising a predetermined function. The axis of abscissa represents the accumulated amount of fuel injected, and the axis of ordinate represents the alcohol concentrations in the fuel tank 20 (upper row) and in the injectors 21 (lower row), respectively.
When fuel of a high alcohol concentration is supplied, upon refueling, to the fuel tank 20 with the accumulated amount of fuel injected (hereinafter referred also to the “accumulated amount of injection fuel) is in a state of “0” in FIG. 13, the alcohol concentration (upper row) in the fuel tank 20 becomes high.
On the other hand, the alcohol concentration (lower row) in the injectors 21 changes with a total delay comprising a dead time Q1 and a first order delay Q2, and the period of this delay (=Q1+Q2) becomes a predetermined accumulated amount of fuel injected.
In the conventional apparatuses as described in the above-mentioned first patent document and the second patent document, a period, after the end of the dead time Q1, in which the alcohol concentration in fuel is changed by the first order delay Q2, is set based on the accumulated amount of injection after refueling, and the alcohol concentration in fuel is estimated in the period thus set.
However, according to the above-mentioned conventional apparatuses, if the dead time Q1 from after refueling until the start of the alcohol concentration change varies, an error will occur in the estimation of the alcohol concentration.
That is, when an error occurs in the setting of the starting time of the alcohol concentration estimation, an appropriate alcohol concentration estimation period and an appropriate update gain of the estimated value can not be set so as to meet the alcohol concentration change behavior of the first order delay Q2, so an error occurs in the alcohol concentration estimation.
In addition, the rate or speed of the alcohol concentration change becomes the largest just after the starting of the alcohol concentration change in view of the behavior of the first order delay Q2, so in case where an error occurs in the starting time of the first order delay Q2, the error in the alcohol concentration estimation becomes large, resulting in an adverse influence on a wide range of internal combustion engine control (e.g., fuel control, ignition control, etc.) in which control constants or parameters are changed in accordance with the estimated value of the alcohol concentration.
Further, since such a variation in the starting time of the alcohol concentration change will be generated due to various factors, it is difficult to set appropriate control constants beforehand in consideration of a variation width or range of the alcohol concentration change starting time.
As a variation factor for the starting time of the alcohol concentration change, there is enumerated, for example, a case in which during the time when the internal combustion engine is in a stopped state, such as during refueling or the like, the fuel in the fuel supply pipe 25 and the delivery pipe 26 is forced to return to the fuel tank 20 under the action of vaporized fuel generated due to the heat transmitted from the internal combustion engine.
In addition, as other variation factors, the following cases are exemplified. That is, a first case is that during the time when the internal combustion engine is stopped for an extended period of time, the fuel in the fuel supply pipe 25 and the delivery pipe 26 returns to the fuel tank 20; a second case is that an error occurs in the calculation of the accumulated amount of injected fuel after refueling; a third case is that the calculated value of the accumulated amount of injected fuel after refueling is reset during the time until the following refueling; a fourth case is that the fuel supply pipe 25 or the delivery pipe 26 or both of them are replaced with a pipe(s) of a different shape(s); a fifth case is that fuel comes out from the fuel pump 22 and/or the fuel tank 20 at the time of the replacement of the fuel supply pipe 25 and/or the delivery pipe 26; and so on.
In the conventional control apparatuses for an internal combustion engine, if the dead time Q1 from after refueling until the start of the alcohol concentration change varies, an error will occur in the estimation of the alcohol concentration, as a result of which there has been a problem that an adverse influence is exerted on the fuel control, etc., which is effected based on the estimated value of the alcohol concentration.